A chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. A fusion gene may be created when the translocation joins two otherwise separated genes, an event which is common in cancer. Cytogenetics and karyotyping of affected cells may be used to detect translocations. There are two main types, reciprocal (also known as non-Robertsonian) and Robertsonian. Also, translocations can be balanced and result in an even exchange of material with no genetic information extra or missing, or unbalanced, having an unequal exchange of chromosome material and sometimes resulting in extra or missing genes or portions thereof. Chromosomal rearrangements are known to contribute to a variety of diseases in humans.
Translocations and inversions are structural abnormalities; other types of chromosomal abnormalities include numerical or copy number changes, for example, extra or missing chromosomes or chromosomal regions and large-scale deletions or duplications. Structural abnormalities can arise from errors during homologous recombination. Both structural and numerical abnormalities can occur in gametes and therefore will be present in all cells of an affected person's body, or they can occur during mitosis and give rise to a genetic mosaic individual who has some normal and some abnormal cells.